Manufacturers of internal combustion engines, particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of nitrogen oxides, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide, particulate matter, and other particulates. In order to reduce the emissions of internal combustion engines, a number of different strategies are being used. For example, exhaust gas recirculation (“EGR”) techniques are utilized in some conventional internal combustion engines to reduce the level of nitrogen oxides in the exhaust gas.
During a cold start of an internal combustion engine, a quantity of emissions from the engine is relatively large compared to a quantity of emissions from the engine after the engine is heated up to a certain temperature. In order to reduce the emissions more effectively during a cold start of the engine, emissions reduction strategies applied during a cold start are different than emissions reduction strategies applied when the engine is warmed up. Some regulation standard requires that the emission reduction strategies be monitored and diagnosed. It is, therefore, desirable to provide methods and systems to monitor and assess cold start emission reduction strategies.